Evaluating the Sensitivity of Fine Nitrate Aerosol Production to Changing Ammonia Emissions in the UK

Atmospheric composition on the regional scale directly effects air quality and in turn has significant implications for human health. Particulate matter (PM) can have a significant effect on health, especially in the fine fraction PM_2.5. It is therefore necessary to examine the sources of such atmospheric constituents and investigate the processes that lead to the degradation of air quality in order to develop effective policy mechanisms to reduce exposure.

While road traffic emissions of particulate matter are well known, additional, more complex, sources such those from agriculture are important during some air pollution episodes and make a significant contribution to particulate levels in the UK and Europe. Ammonia (NH₃) is a precursor gas that can react in the atmosphere and increase aerosol levels through the formation of ammonium nitrate aerosol (NH₄NO₃) - an important component of PM_2.5.

It is of interest to investigate the sensitivity of aerosol predictions to variations in ammonia emissions for two reasons: (i) to estimate the impact of possible errors in emissions inventories and (ii) to give some indication of the likely impact of future ammonia emissions changes on particulate levels. Using the UK Met Office's Air Quality configuration of the Unified Model (AQUM) (Savage et al. 2013), we have studied the sensitivity by varying the ammonia emissions and monitoring the impact on predicted ammonium nitrate aerosol air concentrations close to the surface. Initial results suggest that, in general, the sensitivity is small, suggesting that ammonium nitrate aerosol production is limited by other factors. A more detailed analysis is in preparation and will be presented.